A new technique has arrived on the scene that makes life a little easier for those of you into studying histone turnover rates. Taking advantage of technologies used by our friends in proteomics, researchers at Princeton University explored the turnover of various histone proteins and how post-translational modifications (PTMs) alter the speed of that process.
Previous studies of histone turnover have shown correlations between turnover rate and transcription, but they used radioactive or fluorescent labels and were unable to look at PTMs.To fix those problems, Barry Zee and his team created a new approach that combined stable isotope labeling of amino acids in cell culture (SILAC) with mass spectrometry (MS) allowing them to not only detect individual core histones and PTMs, but also determine how quickly each of those variants is degraded and replaced, or turned over, within a cell population.
Here are some insights that the scientists gained using the new method:
- Histones are, for the most part, very stable proteins.
- H2A variants showed the widest range of turnover rates, and H1.4 was much faster than H3 or H4.
- Acetylated histones are turned over more often than methylated histones
- Active marks have higher turnover than silent ones
- Dual marks (silent and active) on the same peptide leads to a different turnover rate than either mark alone.
These early results have the Princeton authors convinced that there are still more twists in the histone turnover story yet to be revealed and that SILAC provides a unique way to get at them.
Follow all the twists and turnovers at Epigenetics & Chromatin, December 2010.